Conventionally, a combustor which is provided with a pilot nozzle performing diffusion combustion with a pilot light by diffusing fuel gas and a main nozzle performing premixed combustion by mixing air with fuel is employed as a combustor of a gas turbine plant. A gas turbine rotates by utilizing combustion gas from this combustor, and then a generator generates electricity by a motive power of this gas turbine. Consequently, in a power generating facility utilizing a gas turbine, it is possible to control output of a generator by controlling combustion of a combustor.
In controlling combustion of such a combustor as is described above, a fuel ratio of pilot fuel being supplied to the pilot nozzle versus main fuel being supplied to the main nozzle is also controlled. By controlling this fuel ratio to be an appropriate value, it is possible to restrain exhaust amount of NOx. FIG. 6 shows a construction of this conventional combustor controller for controlling a combustor which is equipped with a pilot nozzle and a main nozzle.
A combustor controller 100 in FIG. 6 generates based on an output of a generator 4 a bypass valve control signal, in order to control the opening of a combustor bypass valve 8, which is determined by a bypass valve opening operating section 102, and supplies the signal to a combustor bypass valve 8, so as to control an amount of air being supplied to a combustor 3. Further, this combustor controller 100 generates based on an output of a generator 4 an IGV control signal, in order to control an opening of an inlet guide vane (IGV) 5, which is determined by an IGV opening operation section 103, and supplies the signal to the IVG 5, so as to control an amount of air being supplied to a compressor 1. Here, the bypass valve opening operating section 102 and the IGV opening operating section 103 calculate values of a bypass valve control signal and an IGV control signal based on the graphs in FIG. 3 and FIG. 4. The axes of abscissas in FIG. 3 and FIG. 4 represent an output of a generator.
Further, the combustor controller 100 generates a fuel flow rate instruction signal (CSO) by obtaining a difference between an output of the generator 4 and an aimed generator output in a subtraction section 9 and then adding thereto an integral constituent in PI section 10. When the value of this CSO from the PI section 10 is compared with a predetermined value “L” by using a limiter 11 and is determined to be lower than the predetermined value “L,” the CSO's are supplied to a pilot ratio operating section 101 and a multiplication section 12.
In the pilot ratio operating section 101, a multiplication value used in the multiplication section 12 is set in the multiplication section 12 based on CSO so as to be supplied to the multiplication section 12. In the multiplication section 12, the CSO being supplied by a limiter 11 is multiplied by the multiplication value being supplied by the pilot ratio operating section 101, so as to generate a pilot fuel control signal, which is to be supplied to a pilot fuel control valve 7. Additionally, in a subtraction section 13, a pilot fuel control signal being supplied by the multiplication section 12 is subtracted from the CSO being supplied by the limiter 11, so as to generate a main fuel control signal, which is to be supplied to a main fuel control valve 6. Further, in the pilot ratio operating section 101, a value of a pilot fuel control signal is obtained based on a graph in FIG. 2. Moreover, the axis of abscissas in FIG. 2 represents a CSO value.
In a combustor controller 100 constructed as described above, when a load to a gas turbine 2 is low and an output of a generator 4 is low, in order to restrain combustion vibration and achieve stable combustion, an opening of an IGV 5 is closed so as to decrease the flow rate of air flowing into a compressor 1, and an opening of a combustor bypass valve 8 to increase the flow rate of compressed air flowing directly into the gas turbine 2 from the compressor 1. By decreasing the flow rate of air to the combustor 3 in the above-mentioned manner, a fuel-air ratio is increased. Moreover, when a load to a gas turbine 2 is high and an output of the generator 4 is high, in order to restrain a discharge amount of NOx, the flow rate of air flowing into the compressor 1 is increased by opening the IGV and an amount of compressed air flowing directly into the gas turbine 2 from the compressor 1 is decreased by closing the combustor bypass valve 8. By increasing the flow rate of air being supplied to the combustor 3 in the above-mentioned manner, the fuel-air ratio is decreased.
Further, when an output from a generator is low, in order to activate combustion of a pilot nozzle and restrain combustion vibration, thereby achieving stable combustion, a ratio of pilot fuel (“pilot ratio”) versus entire fuel being supplied to the combustor 3 is increased by closing the main fuel control valve 6 and opening the pilot fuel control valve 7. Also, when an output from a generator is high, in order to restrain combustion of a pilot nozzle and restrain the exhaust amount of NOx, the pilot ratio is decreased by opening the main fuel control valve 6 and closing the pilot fuel control valve 7.
Conventionally, a thermal energy obtained by combustion is converted to a kinetic energy by a gas turbine 2 and this kinetic energy is converted to an electric energy by a generator 4 in the above-mentioned manner. Also, as described above, the output of the generator 4 shows a state which is close to a combustion state in the combustor 3, and response delay to a change of combustion state in the combustor 3 is small. Consequently, as explained above, conventionally, the pilot ratio and the opening of an IGV 5 and combustor bypass valve 8 are set based on an output from a generator 4.
However, because in a conventional combustor controller, a flow rate of air being supplied to a combustor and a flow rate of fuel being supplied to a pilot nozzle and a main nozzle are set based on an output of a generator, accurate control cannot be performed in a case where a power factor of electricity supply system of a generator is changed or in a case where a compound power generation system using a steam turbine at the same time is subject to a rapid load fluctuation.
Namely, in a case where reactive power is increased, resulting in variation of power factor, proportionality relation between a propulsion torque of a gas turbine obtained by combustion and the generator output is broken because the generator output is measured by effective electric power. At this time, because the generator output becomes small although the propulsion torque of a gas turbine does not vary, such a control is performed as increases the pilot ratio and the fuel-air ratio.
Moreover, in a compound power generation facility where a steam turbine is connected to a gas turbine by way of one shaft, the generator output is equivalent to a total of a propulsion torque of a gas turbine and a propulsion torque of a steam turbine. Therefore, the generator output based on the propulsion torque of a gas turbine is obtained by presuming a propulsion torque of a steam turbine in a steady state, and the pilot ratio and the fuel-air ratio are controlled in the combustor based on the generator output which is equivalent to this obtained propulsion torque of a gas turbine. Consequently, the generator output being equivalent to a propulsion torque of a gas turbine is not obtained accurately, and when a rapid load fluctuation occurs, it is impossible to control the pilot ratio and the fuel-air ratio in the combustor accurately.
In order to prevent the above-mentioned problem, it is preferable to control the pilot ratio and the fuel-air ratio in a combustor by temperature of combustion gas at the outlet of the combustor (i.e. temperature of combustion gas being supplied to the inlet of a gas turbine, which is referred as “turbine inlet temperature” hereafter). However, in recent gas turbines, because the turbine inlet temperature exceeds 1500° C., there exist no temperature-measuring devices which can measure the turbine inlet temperature continuously for a long time. Moreover, although there is a method of presuming the turbine inlet temperature by calculating from the casing pressure of a combustor and exhaust gas temperature of a gas turbine, response of exhaust gas temperature to combustion state is bad. As a result, a delayed value is supplied to the actual turbine inlet temperature, which causes a response delay to occur in controlling the pilot ratio and fuel-air ratio in the combustor.